What are the advantages and disadvantages of different particle sizing methods?

Different Sizing

The laser diffraction technique is widely regarded as the most reliable technique for most industrial applications. The measurements are fast, repeatable, accurate, reproducible, and sensitive. It accurately measures the size of irregular as well as regular-shaped particles. It is not affected by the density of a particle or its porosity. It can measure wet, dry, or sprays either in the laboratory or online. The laser diffraction technique can also be combined with dynamic image analysis, providing more accurate measurement results when facing particles whose sizes are related to their orientation to the laser source, such as rod-like particles.

Static and dynamic image analysis is a measurement technique used for measuring particle size, which cover a wide size range with no need to change lenses or other components. In dynamic image analysis, wet and dry samples can be automatically measured with minimal human intervention, which is easy to be used, providing fast analysis and good repeatability, reproducibility, and accuracy.

Dynamic light scattering is primarily used for measuring sub-micron particles. However, for the particles whose sizes are greater than 3μm, dynamic light scattering is unsuitable because they have a failing in that the Brownian motion speed is very low, so low in fact that the sedimentation speed of the particles is greater than the Brownian motion speed.

Gravity sedimentation particle size analysis is a technique that relies on Stokes’ law and has been a very popular method for those applications in which it is applicable. For the calculation of the particle size, the density of the material is necessary. Hence the method is not good for measuring low-density emulsions where the material does not settle or very dense materials which settle quickly. For the particles whose sizes are smaller than 2μm, this technique is limited due to the dominant Brownian motion

Particle Methods

Coulter principle was developed for sizing blood cells which are virtually mono-dispersed suspensions in a dilute electrolyte. Although particle number and volume-based particle size can be given, orifices have to be changed when measuring different samples. Therefore the operation is difficult. Besides, calibration should be carried out regularly.

Light obscuration is a particle counting method that is primarily used for measuring small amounts of contamination in clean room facilities, such as pharmaceutical labs and silicon chip manufacturing facilities. Detection of contamination level in aircraft fuels is an important application as well. So basically, it is a low-concentration detection technique that needs constant calibration and is unsuitable for most industrial applications.

Sieving is an old technique used to separate particles with different size ranges, which is easy to use and cheap. However, the measurement result is greatly affected by human errors.

Scanning electron microscope requires elaborate sample preparation and is slow. Though clear images of particles are provided, there can be large operator-to-operator variability on the same sample because the particles are analyzed manually, and the observation area greatly varies, leading to poor representativeness.

The ultrasonic extinction is primarily used in an online system for the detection of undiluted samples. In reality, it can work for some applications, but it is very expensive. To properly function, it needs to be set up with up to 13 different parameters, which are difficult to be found and sometimes non-existent.

Struggling to grasp particle analysis concepts? Our new Beginner's Guide to Particle Analysis is here to help you grasp these concepts in the most accessible manner possible. Download it as a PDF to read on the train, on the plane, or wherever else there’s no internet.